The present invention relates to a bell mouth which is used by being attached to an opening portion of a pipe used by being connected to a handhole or a manhole which is used as a junction point for electric cables or telephone cables to form an underground conduit line in buried form.
Conventionally, a member which is generally referred to as a bell mouth and whose one end is formed into a tapered tubular form is inserted and fitted in an opening portion of a pipe for forming a conduit line by being connected to a pipe connecting hole in a junction point of this type for electric cables, telephone cables, or the like, e.g., a handhole or a manhole (hereafter, such a junction point will be representatively referred to as the "handhole" or the "handhole or the like"). This member, that is, the bell mouth is used as a compensating means for protecting the pipe opening portion and for smoothly guiding electric cables at the time of insertion of the electric cables into the conduit line.
However, generally, the pipe which is conventionally used by being connected to the handhole or the like is a spirally corrugated pipe, and the bell mouth which is used by being coupled to the opening portion of the spirally corrugated pipe has been known and used for a long time. As for this bell mouth, its spirally corrugated portion which is threadedly engaged with the spirally corrugated portion of the pipe is formed as a tubular portion, and this spirally corrugated portion is inserted into the spiral pipe along the spiral of the pipe while spirally rotating the bell mouth, so as to be inserted and fixed in the opening portion of the pipe.
In the case where the pipe is the spirally corrugated pipe as described above, the bell mouth is structured such that it is also provided with the spirally corrugated portion which is threadedly engaged with the spirally corrugated portion of the pipe, so that the bell mouth can be coupled firmly to the pipe by being screwed in so as not to come off the pipe.
However, in a case where the pipe is not the spirally corrugated pipe but an annularly corrugated pipe, since the bell mouth cannot be screwed into the pipe, it is difficult to firmly couple the bell mouth to the pipe so as not to come off the pipe. For this reason, such a coupling method has not generally been practiced. On the other hand, among the pipes, there are not only spirally corrugated pipes but also annually corrugated pipes. As such, there is naturally a large latent demand for using such annually corrugated pipes as pipes to be connected to the handholes or the like.